This invention relates to video recording, and more particularly, to a digital video recording system for use at Point of Sale (POS) locations, Automated Teller Machines (ATM's), and other locations where the monitoring of activities is important.
Video recording equipment is in common use throughout industry and commerce. Conventional video recording systems are analog systems employing a video recorder which records images on a magnetic tape. The recorder used is a slow scan recorder whose video input is provided by a camera located at the POS or ATM. Recording is typically continuous over a predetermined period which is typically 24 hours. If nothing of significance occurs during the recording period, the tape is simply rerun again through the recorder with the prior recorded images being recorded over.
This process has a number of problems associated with it. In most installations, most of the time, nothing ever happens. Rather, the same tape is used over and over with the same background image being recorded over and over. Only if something of significance happens is the tape removed and replaced. Preferably, each tape should be removed, degaussed, and reinserted in the recorder at the end of each recording interval. Or, each tape is changed every day with the tape removed being degaussed before its next use. However, this is seldom done because of the expense or impracticality of doing so.
Because the same images are continuously being recorded, over time, the magnetic particles in the tape tend to align themselves in a particular orientation consistent with those images. This residual magnetization degrades the resolution capability of the tape and resulting quality of the recorded images. One problem law enforcement officers or security personnel have with the recording systems described above is that the poor quality of the recorded images makes it difficult to discern features or details of the events captured on the tape, including the identification of persons.
Another problem with conventional recording systems is that simply because an event of significance has occurred, recording does not stop. Thus, in order to view the event, it is necessary to rewind the tape and scan through it to the place where the event is recorded. In situations where time may be critical, the resulting delay is very undesirable.
U.S. Pat. No. 5,996,023 to Winter et al. teaches the use of circular pre-alarm buffering at high frame rates. The circular pre-alarm buffer is used to delay a signal until a set time has passed and a decision can be made as to the occurrence of an activity of interest. The circular pre-alarm buffer is continuously overwritten unless an alarm input triggers the contents to be marked for permanent storage. In this manner, high frame rate recordings (15 fps or more) can be made during the time of interest. The '023 Winter et al. patent specifically rejects the use of continuous recording at low frame rates (e.g. 1 fps) as outlined as possibly missing important data. The teachings of the '023 Winter et al. patent also discuss the detection of motion. However, there is no indication of how the motion detection is performed and specifically, the motion is not used to aid in the size reduction of the stored data. It is used to provide event related information for storage with the image.
U.S. Pat. No. 5,371,551 to Logan et. al teaches the use of a buffer to provide a time delay in viewing stored images with pause, reverse, and thumbnail functions. The '551 Logan et al. patent also teaches that read-out rates may be different than input rates to accommodate a limited storage capacity. The '551 Logan et al. system cannot be readily adapted to systems with a large or unlimited storage capacity configured for continuous activity recording.
U.S. Pat. No. 6,101,276 to Adiletta teaches the detection of motion through comparison with a reference image, using macro blocks to determine two types of macro block coding, spatial and temporal. Spatial blocks are coded by encoding the raw block itself. Temporal blocks are coded by finding motion vectors relative to a reference block and then encoding the error between the reference block and the temporal block. The blocks are encoded by comparing them to reference images and assigning a code to each block. The complexity of the identification of motion vectors is processor intensive, and the use of these operations requires specialized hardware, with some of the processing being done in software.
U.S. Pat. No. 6,125,145 to Koyanagi also teaches the use of motion detection using a complex algorithm for brightness and color information. The '145 Koyanagi patent further teaches the use of motion range detection at various distances from the camera using a plurality of ranges. The '145 Koyanagi patent uses of one of three operator selected methods for updating the reference image, unconditional, conditional, or none. Reliance upon an operator selected method for updating a reference image introduces a source of error into the system, as the environmental conditions in an image field may change such that the update method originally selected by the operator is no longer the best method.
U.S. Pat. No. 5,731,832 to Ng teaches the generation of a difference matrix of average differences between reference-frame macro blocks and current-frame macro blocks to detect motion. This may be used for intrusion detection. As an ancillary function, the current image is recorded if the difference matrix profile exceeds a threshold. Of note is that the entire image is recorded rather than only the difference portions as in the present invention. Also, only the image containing the detected motion is recorded and there is no continuous recording of image data, which may cause the loss of important context information contained in either previous of subsequent image frames.
Finally, U.S. Pat. No. 5,229,850 to Toyoshima teaches the use of an external sensor to detect the occurrence of an event to be monitored and to trigger the recording of an image associated with the event, adding to the complexity of the system.